1. Field of the Invention
The invention relates to a method for generation of electromagnetic radiation. Furthermore, the invention relates to an optical frequency synthesizer.
2. The Prior Art
For different applications, for example in the field of optical spectroscopy, there is a need for light sources that are able to generate electromagnetic radiation having a predeterminable frequency. In this connection, it should be possible to adjust the frequency with great precision. In particular, there is a need for light sources that can be tuned over a broad bandwidth, in which the frequency can be freely predetermined within the available tuning range, whereby the predetermined frequency is known with great precision.
For example, it is known to couple the frequency of the radiation of a continuous-wave laser with the frequency of a spectral line of an optical frequency comb used as the frequency standard, by means of suitable regulation. A suitable regulator regulates the frequency by optical phase regulation, in such a manner that the frequency distance between the selected spectral line of the optical frequency comb and the shifted frequency of the main beam is given a predetermined value. This frequency distance is changed in order to obtain a desired frequency. If the frequency distance approaches half the distance between the spectral lines of the frequency comb, it is impossible to select the correct spectral line of the frequency comb. Therefore, setting just any desired frequency in the tuning range is also not possible. In order to solve this problem, an optical frequency shifter can be used in the useful beam of the continuous-wave laser. This method makes it possible to set more or less any desired frequencies with great precision. However, continuous tuning of the frequency of the continuous-wave laser continues to be impossible. Furthermore, it is disadvantageous that additional losses, amplitude modulations, and a beam offset in the main beam of the continuous-wave laser occur.
Another known approach is to couple the frequency of a continuous-wave laser, similar to what was described above, with a spectral line of an optical frequency comb, whereby then, the optical frequency comb is detuned in order to tune the frequency. It is true that the possibilities in frequency tuning are improved. However, this method makes it impossible to couple multiple light sources with a single optical frequency comb, independent of one another. As a result, various interesting areas of application are excluded. Furthermore, implementation of a highly precise and tunable frequency comb is complicated and difficult.